Hint

Answer

D, D

These are the first letters of the names of the trains whose numbers are 1 through 10 on the Island of Sodor in the television series "Shining Time Station": Thomas, Edward, Henry, Gordon, James, Percy, Toby, Duck, Donald, Douglas.
"(also known as Thomas the Tank Engine and Friends)
Based on the Railway Series by The Rev. W. Awdry